Methods of Treating a Silicon Carbide Substrate for Improved Epitaxial Deposition and Resulting Structures and Devices

ABSTRACT

A method is disclosed for treating a silicon carbide substrate for improved epitaxial deposition thereon and for use as a precursor in the manufacture of devices such as light emitting diodes. The method includes the steps of implanting dopant atoms of a first conductivity type into the first surface of a conductive silicon carbide wafer having the same conductivity type as the implanting ions at one or more predetermined dopant concentrations and implant energies to form a dopant profile, annealing the implanted wafer, and growing an epitaxial layer on the implanted first surface of the wafer.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims priority fromprovisional application Serial No. 60/355,034 filed Feb. 8, 2002.

BACKGROUND OF INVENTION

[0002] To date, the most successful materials for producing lightemitting devices or “LEDs” (including light emitting diodes, laserdiodes, photodetectors and the like) capable of operation in the UV,blue and green portions of the electromagnetic spectrum have been thegroup III-nitride compound semiconductor materials, and in particulargallium nitride-based compound semiconductors. However, gallium nitridepresents a particular set of technical problems in manufacturing workingdevices. The primary problem is the lack of bulk single crystals ofgallium nitride which in turn means that gallium nitride or other groupIII-nitride devices must be formed as epitaxial layers on othermaterials. Sapphire (i.e., aluminum oxide or Al₂O₃) has been commonlyused as a substrate for group III-nitride devices. Sapphire offers areasonable crystal lattice match to Group III nitrides, thermalstability, and transparency, all of which are generally useful inproducing a light emitting diode. Sapphire offers the disadvantage,however, of being an electrical insulator. This means that the electriccurrent that is passed through an LED to generate the emission cannot bedirected through the sapphire substrate. Thus, other types ofconnections to the LED must be made, such as placing both the cathodeand anode of the device on the same side of the LED chip in a so-called“horizontal” configuration. In general, it is preferable for an LED tobe fabricated on a conductive substrate so that ohmic contacts can beplaced at opposite ends of the device. Such devices, called “vertical”devices, are preferred for a number of reasons, including their easiermanufacture as compared to horizontal devices.

[0003] In contrast to sapphire, silicon carbide can be conductivelydoped, and therefore can be effectively used to manufacture a verticalgroup III-nitride LED. In addition, silicon carbide has a relativelysmall lattice mismatch with gallium nitride, which means thathigh-quality group III-nitride material can be grown on it. Siliconcarbide also has a high coefficient of thermal conductivity, which isimportant for heat dissipation in high-current devices such as laserdiodes.

[0004] Examples of silicon carbide-based group III-nitride LEDs areshown in U.S. Pat. Nos. 5,523,589, 6,120,600 and 6,187,606 each of whichis assigned to Cree, Inc., the assignee of the present invention, andeach of which is incorporated herein by reference. Such devicestypically comprise a silicon carbide substrate, a buffer layer or regionformed on the substrate, and a plurality of group III-nitride layersforming a p-n junction active region.

[0005] In particular, U.S. Pat. No. 6,187,606 represents an importantadvance over the state of the art as it previously existed. Theinvention described in the '606 patent provided a plurality of discretecrystal portions, or “dots,” of GaN or InGaN on the substrate in anamount sufficient to minimize or eliminate the heterobarrier between thesubstrate and the buffer layer. A highly conductive path between thesubstrate and the active region could thereby be established.

[0006] An important parameter for LEDs is the forward voltage (V_(f))drop between the anode and the cathode of the device during forward biasoperation. In particular, it is desirable for the forward voltage(V_(f)) of a device to be as low as possible to reduce power consumptionand increase the overall efficiency of the device. Despite the advanceof the '606 patent, there remains a measurable voltage drop at theinterface between a conventional silicon carbide substrate and theconductive buffer layer. It is desirable to reduce this voltage drop inorder to reduce the overall V_(f) of the resulting device.

DETAILED DESCRIPTION

[0007] Methods according to embodiments of the present invention includethe steps of providing a SiC wafer having a predetermined conductivitytype and first and second surfaces; implanting dopant atoms of thepredetermined conductivity type into the first surface of the SiC waferat one or more predetermined dopant concentrations and implant energiesto form a dopant profile; annealing the implanted wafer; and growing anepitaxial layer on the implanted first surface of the substrate. Othermethods according to embodiments of the present invention include thesteps of providing a SiC wafer having a predetermined conductivity typeand first and second surfaces; forming a capping layer on the firstsurface of the wafer; implanting dopant atoms of the predeterminedconductivity type into the capping layer and the first surface of theSiC wafer at one or more predetermined dopant concentrations and implantenergies to form a dopant profile; annealing the implanted wafer;removing the capping layer; and growing an epitaxial layer on theimplanted first surface of the substrate.

[0008] Structures according to embodiments the present invention includea silicon carbide substrate having a predetermined conductivity type andhaving first and second surfaces with a first implantation profile ofimplanted dopants of the predetermined conductivity type adjacent thefirst surface and an epitaxial layer grown on the first surface.

[0009] Devices according to embodiments of the present invention includea light emitting device comprising a silicon carbide substrate having apredetermined conductivity type and first and second surfaces, aconductive buffer layer on the first surface of the substrate, and anactive region on the conductive buffer, wherein the first surface of thesubstrate has a first implantation profile of implanted dopants of thepredetermined conductivity type adjacent the first surface.

[0010] Referring to FIG. 1 which shows a simplified schematic of asilicon carbide-based LED according to the present invention, device 10comprises a conductive silicon carbide substrate 12 having a firstconductivity type and having a first surface 12A and a second surface12B. Device 10 further includes a conductive buffer region 14 formed onsurface 12A of substrate 12 and an active region 18 formed on theconductive buffer 14. Active region 18 preferably includes a p-njunction and most preferably comprises a single heterostructure, doubleheterostructure, single quantum well, multiple quantum well or the like.A first ohmic contact 22 is formed on the surface of the active region.A second ohmic contact 24 is formed on the surface of the substrate 24.In a preferred embodiment, substrate 12 comprises n-type 4H-siliconcarbide. Accordingly, in a preferred embodiment ohmic contact 22comprises the anode of the device 10 while ohmic contact 24 comprisesthe cathode of the device 10. Ohmic contact 24 may be formed accordingto the methods described in U.S. patent application Ser. No. 09/787,189filed Mar. 15, 2001 which is incorporated herein by reference. Substrate12 includes a first implanted region 20 adjacent to surface 12A andcomprising implanted dopant atoms of the first conductivity type. Thepresence of implanted region 20 causes a reduction in the voltage dropobservable at the interface between substrate 12 and buffer region 14,which results in a reduction in the overall forward operating voltage(V_(f)) of the device 10. The implanted region has a peak concentrationof implanted dopant atoms of between about 1E19 and 5E21 cm⁻³ and isbetween about 10 and 5000 Å thick. Preferably, the implanted region hasa peak concentration of implanted dopant atoms of about 1E21 cm⁻³ and isabout 500 Å thick.

[0011]FIG. 2 illustrates a method of fabrication of structures accordingto the present invention. A silicon carbide substrate 12 is providedhaving a first conductivity type and having first surface 12A and secondsurface 12B. The fabrication of doped silicon carbide substrates such assubstrate 12 is well known in the art. For example, U.S. Pat. RE34,861discloses a process for growing boules of silicon carbide via controlledseeded sublimation. The resulting silicon carbide crystal may exhibitone of a number of polytypes, such as 4H, 6H, 15R or others. N-typedopants such as nitrogen and/or phosphorus or p-type dopants such asaluminum and/or boron may be incorporated into the crystal during growthto impart a net n-type or p-type conductivity, respectively. The crystalboules are then sliced into wafers which are chemically and mechanicallytreated (polished) to provide a suitable substrate for the growth ofepitaxial layers and the fabrication of electronic devices thereon.

[0012] In a preferred embodiment, substrate 12 comprises n-type 4H or6H-silicon carbide doped with nitrogen donor atoms at a net dopantconcentration of about 5E17 to 3E18 cm⁻². Subsequent to wafering andpolishing, dopant atoms 30 of a predetermined conductivity type areimplanted into surface 12A of substrate 12 at one or more predetermineddopant concentrations and implant energies to form a dopant profile inimplanted region 20 of substrate 12. Preferably, dopant atoms 30 havethe same conductivity type as substrate 12. That is, if substrate 12 isn-type, then dopants 30 comprise a dopant such as nitrogen and/orphosphorus that imparts n-type conductivity in silicon carbide.Alternatively, if substrate 12 is p-type, then dopants 30 comprise adopant such as boron or aluminum that imparts p-type conductivity insilicon carbide.

[0013] Dopants 30 are implanted into substrate 12 through surface 12Aaccording to an predetermined implant dose and energy level.Implantation may be performed in one step at a single dose and energylevel or in a plurality of steps at multiple doses and/or multipleenergy levels. In a preferred embodiment, implantation is performed viaa plurality of implant doses and energy levels in order to impart arelatively flat implantation profile to a predetermined depth withinsubstrate 12. For example, in one embodiment, a 6H-silicon carbidesubstrate is implanted with phosphorus atoms at a first dose of 2E15cm⁻² and an energy of 25 keV and a second dose of 3.6E15 cm⁻² at anenergy of 50 keV.

[0014] A schematic of a desired depth profile that could be formedaccording to this embodiment is shown the graph of FIG. 4. The graph ofFIG. 4 shows the profile of implanted atoms in atoms/cm³ (y-axis) as afunction of depth in angstroms from the first surface 12A of substrate12 (x-axis). As shown in FIG. 4, the implant profile increases to amaximum of about 1E21 cm⁻³ at a depth of about 300 Å. From there, theprofile stays relatively flat to a depth of about 800 Å, and then beginsto drop off to background levels. Accordingly, implanted region 20 maybe said to extend from surface 12A into substrate 12 for a depth ofabout 800-1000 Å.

[0015] Following the implantation, the substrate is annealed in astandard tube anneal in Argon at a temperature of 1300° for 90 minutesto activate the implanted dopants. A range of temperatures is alsoeffective for annealing, with 1300° being exemplary rather thanlimiting.

[0016] A conductive buffer 14 may then formed on surface 12A ofsubstrate 12.

[0017] One drawback of this embodiment is that the dopant profile tendsto reach its maximum at some depth within the substrate, determined bythe implant doses and energies. That is, the implant concentration atthe surface is less than the maximum concentration within the substrate.Implanted dopant concentrations must be kept at less than about 5E21cm⁻³ or else the implanted atoms will cause unwanted and irreparabledamage to the crystal lattice of substrate 12.

[0018] In order to provide the maximum improvement in voltage drop, itis desirable to have the implant concentration at the surface at thesurface of the substrate at as high a level as possible, i.e., theimplant concentration at the surface should be around 1E21 cm⁻³.However, in order to achieve such a surface concentration according tothe embodiment of FIG. 2, it would be necessary to implant the dopantatoms at a dose and energy level that would produce dopantconcentrations within the substrate that would damage the substrate asdescribed above.

[0019] Accordingly, in another embodiment of the invention illustratedin FIG. 3, a capping layer 32 is deposited on surface 12A of substrate12 prior-to dopant implantation. Preferably, capping layer 32 comprisesa silicon nitride layer or a silicon dioxide layer deposited usingPlasma-Enhanced Chemical Vapor Deposition (PECVD) or grown as a thermaloxide, both of which are well known processes capable for depositingoxide layers of precise thickness and composition. Capping layer 32 mayalso comprise any other suitable material that may be controllablydeposited in thin layers, is susceptible to ion implantation and can beremoved without damaging the underlying surface. Other possiblematerials for capping layer 32 include a metal layer or an epitaxialsemiconductor layer.

[0020] The thickness of capping layer 32 and the implantation parameters(dose and energy) are selected such that the maximum implantconcentration resulting from the implantation step occurs at or near thesurface 12A of the substrate 12 (i.e., at or near the interface betweensubstrate 12 and capping layer 32). The resulting structure is thenannealed in a standard tube anneal in argon at a temperature of 1300° C.for 90 minutes to activate the implanted dopants. Capping layer 32 isremoved using conventional techniques. For example, if capping layer 32comprises a PECVD oxide layer, it may be removed with a wet chemicaletch process. The resulting structure then ideally comprises a substrate12 having an implanted region 20 wherein the peak concentration ofimplanted atoms in the implanted region 20 occurs at or near surface 12Aof substrate 12.

[0021] A schematic of the desired depth profile that could be formedaccording to this embodiment is shown the graph of FIG. 5. The graph ofFIG. 5 shows a schematic profile of implanted atoms in atoms/cm3(y-axis) as a function of depth in angstroms from the first surface 12Aof substrate 12. As shown in FIG. 4, the implant profile isapproximately 1E21 cm⁻³ at a the surface 12A of the substrate 12. Fromthere, the profile stays relatively flat for a depth of about 500 A, andthen begins to drop off to background levels.

[0022] In one embodiment, a silicon dioxide layer 32 having a thicknessof about 500 A is formed via PECVD on surface 12A of substrate 12.Nitrogen atoms are implanted into the oxide layer and the substrate 12in a first dose at an implant energy of 25 keV and a second dose at animplant energy of 50 keV. The first implant may have a dose of about4E12 cm⁻² to 1E15 cm⁻², while the second implant hay have a dose ofabout 7E12 cm⁻² to 1.8E15 cm⁻².

[0023] A graph of the interfacial voltage (V_(f)) at thesubstrate/buffer region interface versus 25 keV implant dose is shown inFIG. 6. To generate the data shown in FIG. 6, sample 4H and 6H siliconcarbide wafers having a net concentration of nitrogen dopants of between3.3E17 and 2.1E18 cm⁻³ were employed. A 500 Å thick PECVD silicondioxide layer was formed on the surface of the wafers, and the waferswere implanted with various controlled doses of nitrogen at energylevels of 25 keV and 50 keV respectively. The implant doses and energylevels for each wafer are shown in Table I. TABLE 1 25 keV Dose 50 keVDose Wafer Type Dopant per square cm (per square cm) A 4H 28N2+ 2.5E144.38E14 B 4H 28N2+ 3.0E14 5.25E14 C 4H 28N2+ 3.5E14 6.13E14 D 4H 28N2+4.0E14  7.0E14 E 6H 28N2+ 2.5E14 4.38E14 F 6H 28N2+ 3.0E14 5.25E14 G 6H28N2+ 3.5E14 6.13E14

[0024] Conductive buffers were then formed on the implanted substrates.The interfacial voltage (i.e., the voltage drop attributable to thesubstrate/buffer interface) was measured at three locations on the waferand an average value was calculated. The average values are plottedagainst the 25 keV implant dose in FIG. 6. As shown in FIG. 6, theinterfacial voltage of the substrate/buffer interface decreases withincreasing dosage.

1. A method of treating a silicon carbide substrate for improved epitaxial deposition thereon and for use as a precursor in the manufacture of devices such as light emitting diodes, the method comprising: implanting dopant atoms of a first conductivity type into the first surface of a conductive silicon carbide wafer having the same conductivity type as the implanting ions at one or more predetermined dopant concentrations and implant energies to form a dopant profile; annealing the implanted wafer; and growing an epitaxial layer on the implanted first surface of the wafer.
 2. The method according to claim 1 wherein the step of implanting dopant atoms comprises carrying out a plurality of implanting steps at varying doses and energy levels in order to impart a relatively flat implantation profile to a predetermined depth within the wafer.
 3. The method according to claim 2 wherein the implanting step comprises implanting dopant atoms in the implant region to a peak concentration of implanted dopant atoms of between about 1E19 and 5E21 cm⁻³.
 4. The method according to claim 2 wherein the implanting step comprises implanting dopant atoms in the implant region to a peak concentration of implanted dopant atoms of about 1E21 cm⁻³ and to a depth within the silicon carbide wafer of about 500 Angstroms.
 5. The method according to claim 2 wherein the implanting step comprises implanting the silicon carbide wafer with phosphorus donor atoms at a first dopant concentration of 2E15 cm⁻² and an implant energy of 25 keV and a second dopant concentration of 3.6E15 cm⁻² at an implant energy of 50 keV.
 6. The method according to claim 1 wherein the implanted wafer is annealed to activate the implanted dopants.
 7. The method according to claim 6 wherein the implanted wafer is annealed in Argon at a temperature of 1300° C. for 90 minutes.
 8. The method according to claim 1 comprising implanting dopant atoms selected from the group consisting of nitrogen and phosphorus into an n-type silicon carbide wafer.
 9. The method according to claim 1 comprising implanting dopant atoms selected from the group consisting of boron and aluminum into a p-type silicon carbide wafer.
 10. A method of treating a silicon carbide substrate for improved epitaxial deposition suitable for use as a precursor in the manufacture of light emitting diodes, the method comprising: forming a capping layer on the first surface of a conductive silicon carbide wafer from a material that can be controllably deposited in thin layers, can be implanted with ions having the same conductivity as the silicon carbide wafer, and can be removed without substantially damaging the underlying surface of the wafer; implanting dopant atoms of a first conductivity type into and through the capping layer and into the silicon carbide wafer at one or more predetermined dopant concentrations and implant energies to form a dopant profile; annealing the implanted wafer; removing the capping layer; and growing an epitaxial layer on the implanted first surface of the substrate wafer.
 11. The method according to claim 10 comprising forming the capping layer from the group consisting of silicon nitride, silicon dioxide, and a metal layer.
 12. A method according to claim 11 comprising depositing the capping layer on the silicon carbide wafer using plasma-enhanced chemical vapor deposition.
 13. A method according to claim 11 comprising growing the capping epitaxial layer on the silicon carbide wafer as a thermal oxide.
 14. The method according to claim 10 comprising growing the thickness of the capping layer and selecting the implant concentration and the implant energy to maximize the implant concentration resulting from the implantation step at or near the interface of the silicon carbide wafer and the capping layer.
 15. The method according to claim 10 comprising forming the capping layer from silicon dioxide and to a thickness of about 500 Angstroms.
 16. The method according to claim 15 comprising implanting nitrogen atoms into and through the silicon dioxide layer and into the silicon carbide wafer in a first dose with a dopant concentration of between about 4E12 cm⁻² and 1E15 cm⁻² at an implant energy of 25 keV and a second dose with a dopant concentration of between about 7E12 cm⁻² and 1.8E15 cm⁻² at an implant energy of 50 keV.
 17. The method according to claim 10 comprising annealing the implanted wafer to activate the implanted dopants.
 18. The method according to claim 17 comprising annealing the implanted wafer is annealed in Argon at a temperature of 1300° C. for 90 minutes.
 19. The method according to claim 10 comprising removing the capping layer with a wet chemical etch process.
 20. A method of treating a silicon carbide substrate for improved epitaxial deposition suitable for use as a precursor in the manufacture of light emitting diodes, the method comprising: forming a capping layer of silicon dioxide on the first surface of a conductive silicon carbide wafer; implanting dopant atoms of the a first conductivity type into and through the silicon dioxide layer and into the silicon carbide wafer at one or more predetermined dopant concentrations and implant energies to form a dopant profile; annealing the implanted wafer; and removing the capping layer.
 21. The method according to claim 20 comprising growing the thickness of the silicon dioxide layer and selecting the implant concentration of dopant atoms and the implant energy to maximize the implant concentration resulting from the implantation step at or near the interface of the silicon carbide wafer and the silicon dioxide layer.
 22. The method according to claim 21 comprising forming the silicon dioxide layer to a thickness of about 500 Angstroms.
 23. The method according to claim 20 comprising implanting nitrogen atoms into and through the silicon dioxide layer and into the silicon carbide wafer in a first dose with a dopant concentration of between about 4E12 cm⁻² and 1E15 cm⁻² at an implant energy of 25 keV and a second dose with a dopant concentration of between about 7E12 cm⁻² and 1.8E15 cm⁻² at an implant energy of 50 keV.
 24. The method according to claim 20 comprising annealing the implanted wafer in Argon at a temperature of 1300° C. for 90 minutes.
 25. The method according to claim 20 comprising removing the silicon dioxide layer with a wet chemical etch process.
 26. A silicon carbide structure suitable for use as a substrate in the manufacture of electronic devices such as light emitting diodes comprising: a silicon carbide wafer having a first and second surface and having a predetermined conductivity type and an initial carrier concentration; a region of implanted dopant atoms extending from said first surface into said silicon carbide wafer to a predetermined depth, said region having a higher carrier concentration than said initial carrier concentration in the remainder of said wafer; and an epitaxial layer on said first surface of said silicon carbide wafer.
 27. A silicon carbide structure according to claim 26 wherein said silicon carbide wafer comprises n-type 6H-silicon carbide.
 28. A silicon carbide structure according to claim 27 wherein said silicon carbide wafer is doped with nitrogen donor atoms.
 29. A silicon carbide structure according to claim 28 having a concentration of said nitrogen donor atoms of between about 5E17 and 3E18 cm⁻².
 30. A silicon carbide structure according to claim 26 wherein said region of implanted dopant atoms comprises phosphorus in a concentration of between about 1E19 and 5E21 cm⁻³.
 31. A silicon carbide structure according to claim 30 wherein said region of implanted dopant atoms comprises phosphorus in a concentration of about 1E21 cm⁻³.
 32. A silicon carbide structure according to claim 26 wherein said region of implanted dopant atoms comprises nitrogen in a concentration of between about 1E19 and 5E21 cm⁻³.
 33. A silicon carbide structure according to claim 32 wherein said region of implanted dopant atoms comprises phosphorus in a concentration of about 1E21 cm⁻³.
 34. A silicon carbide structure according to claim 26 wherein said silicon carbide wafer comprises n-type 4H-silicon carbide.
 35. A silicon carbide structure according to claim 26 wherein said region of implanted dopant atoms extends from said first surface into said silicon carbide wafer to a depth of between about 10 and 5000 Angstroms.
 36. A silicon carbide structure according to claim 35 wherein said region of implanted dopant atoms extends from said first surface into said silicon carbide wafer to a depth of between about 800 and 1000 Angstroms.
 37. A silicon carbide structure according to claim 35 wherein said region of implanted dopant atoms has a peak concentration of implanted dopant atoms of between about 1E19 and 5E21 cm⁻³.
 38. A silicon carbide structure according to claim 37 wherein said region of implanted dopant atoms has a peak concentration of implanted dopant atoms of about 1E21 cm⁻³ and extends from said first surface into said silicon carbide wafer to a depth of about 500 Angstroms.
 39. A silicon carbide structure according to claim 26 wherein the peak concentration of implanted atoms in said implanted region occurs at or near the first surface of said silicon carbide substrate.
 40. A silicon carbide precursor structure suitable for use as a substrate in the manufacture of electronic devices such as light emitting diodes comprising: a silicon carbide wafer having a first and second surface and having a predetermined conductivity type and an initial carrier concentration; a capping layer on said first surface of said silicon carbide wafer formed of a material that can be controllably deposited in thin layers, can be implanted with ions having the same conductivity as the silicon carbide wafer, and can be removed without substantially damaging the underlying surface of the wafer; and a region of implanted dopant atoms extending completely through said capping layer and through said first surface into said silicon carbide wafer to a predetermined depth, said region having a higher carrier concentration than the initial carrier concentration in the remainder of said wafer.
 41. A silicon carbide structure according to claim 40 wherein said capping layer comprises a material selected from the group consisting of silicon nitride, silicon dioxide, and a metal.
 42. A silicon carbide structure according to claim 40 and further comprising an epitaxial thermal oxide layer on said silicon carbide wafer.
 43. A silicon carbide structure according to claim 41 wherein said capping layer has a thickness of about 500 Angstroms.
 44. A silicon carbide structure according to claim 41 wherein the thickness of said capping layer is selected to maximize the implant concentration resulting from implanting dopant atoms into and through said capping layer and into said silicon carbide wafer at or near said first surface of said wafer.
 45. A silicon carbide structure according to claim 40 wherein said region of implanted dopant atoms has a concentration of dopant atoms of about 1E21 cm⁻³ and extends from said first surface into said wafer to a depth of about 500 Angstroms.
 46. A silicon carbide precursor structure suitable for use as a substrate in the manufacture of electronic devices such as light emitting diodes comprising: a silicon carbide wafer having a first and second surface and having a predetermined conductivity type and an initial carrier concentration; a layer of silicon dioxide on said first surface of said silicon carbide; and a region of implanted dopant atoms extending completely through said silicon dioxide layer and through said first surface into said silicon carbide wafer to a predetermined depth, said region having a higher carrier concentration of dopant atoms than the initial carrier concentration in the remainder of said wafer.
 47. A silicon carbide structure according to claim 46 wherein said layer of silicon dioxide is about 500 Angstroms thick.
 48. A silicon carbide structure according to claim 46 wherein said implanted dopant atoms are nitrogen in a concentration of about 1E21 cm⁻³ wherein said region of implanted dopant atoms extends from said first surface into said silicon carbide wafer to a depth of about 500 Angstroms.
 49. A method of forming a light emitting diode comprising the steps of: implanting dopant atoms of a first conductivity type into the first surface of a conductive silicon carbide wafer having the same conductivity type as the implanting ions at one or more predetermined dopant concentrations and implant energies to form a dopant profile; annealing the implanted wafer; forming a conductive buffer region on the implanted first surface of the silicon carbide wafer; forming an active region on the conductive buffer region; forming a first ohmic contact on said active region; and forming a second ohmic contact on the second surface of said silicon carbide wafer.
 50. The method according to claim 49 further comprising the step of fabricating the active layer as a single heterostructure.
 51. The method according to claim 49 further comprising the step of fabricating the active layer as a double heterostructure.
 52. The method according to claim 49 further comprising the step of fabricating the active layer as a single quantum well.
 53. The method according to claim 49 further comprising the step of fabricating the active layer as a multiple quantum well.
 54. The method according to claim 49 further comprising carrying out a plurality of implanting steps at varying doses and energy levels in order to impart a relatively flat implantation profile to a predetermined depth within the wafer.
 55. The method according to claim 54 further comprising implanting dopant atoms in the implant region to a peak concentration of implanted dopant atoms of between about 1E19 and 5E21 cm⁻³.
 56. The method according to claim 54 further comprising implanting dopant atoms in the implant region to a peak concentration of implanted dopant atoms of about 1E21 cm⁻³ and a thickness of about 500 Angstroms.
 57. The method according to claim 49 further comprising implanting the silicon carbide wafer with phosphorus donor atoms at a first dopant concentration of 2E15 cm⁻² and an implant energy of 25 keV and a second dopant concentration of 3.6E15 cm⁻² at an implant energy of 50 keV.
 58. The method according to claim 49 comprising annealing the implanted wafer is annealed to activate the implanted dopants.
 59. The method according to claim 58 comprising annealing the implanted wafer in Argon at a temperature of 1300° C. for 90 minutes.
 60. A light emitting diode (“LED”) comprising: a silicon carbide wafer having a first and second surface and having a predetermined conductivity type and an initial carrier concentration; a region of implanted dopant atoms extending from said first surface into said silicon carbide wafer for a predetermined distance, said region having a higher carrier concentration than said initial carrier concentration in the remainder of said wafer; a conductive buffer region on said first surface of said conductive silicon carbide wafer; an active region on said conductive buffer region; a first ohmic contact to said active region; and a second ohmic contact on the second surface of said silicon carbide wafer.
 61. An LED according to claim 60 wherein said active layer is a single heterostructure.
 62. An LED according to claim 60 wherein said active layer is a double heterostructure.
 63. An LED according to claim 60 wherein said active layer is a single quantum well.
 64. An LED according to claim 60 wherein said active layer is a multiple quantum well.
 65. An LED according to claim 60 wherein said silicon carbide wafer comprises n-type 6H-silicon carbide.
 66. An LED according to claim 65 wherein said initial carrier concentration of said silicon carbide wafer comprises nitrogen.
 67. An LED according to claim 66 wherein said carrier concentration of said nitrogen is about 5E17 to 3E18 cm⁻³.
 68. An LED according to claim 65 wherein said initial carrier concentration of said silicon carbide wafer comprises phosphorus.
 69. An LED according to claim 60 wherein said region of implanted dopant atoms comprises phosphorus atoms with an implant concentration of between about 1E19 and 5E21 cm³¹ ³.
 70. An LED according to claim 69 wherein said region of implanted dopant atoms comprises phosphorus dopant atoms with an implant concentration of about 1E21 cm⁻³.
 71. An LED according to claim 60 wherein said region of implanted dopant atoms comprises nitrogen dopant atoms with an implant concentration of between about 1E19 and 5E21 cm⁻³.
 72. An LED according to claim 71 wherein said region of implanted dopant atoms comprises phosphorus atoms with an implant concentration of about 1E21 cm⁻³.
 73. An LED according to claim 60 wherein said silicon carbide wafer comprises n-type 4H-silicon carbide.
 74. An LED according to claim 60 wherein said region of implanted dopant atoms extends from said first surface into said silicon carbide wafer to a depth of between about 10 and 5000 Angstroms.
 75. An LED according to claim 60 wherein said region of implanted dopant atoms extends from said first surface into said silicon carbide wafer to a depth of between about 800 and 1000 Angstroms.
 76. An LED according to claim 60 wherein said region of implanted dopant atoms has a peak concentration of implanted dopant atoms of between about 1E19 and 5E21 cm⁻³.
 77. An LED according to claim 76 wherein said region of implanted dopant atoms has a peak concentration of implanted dopant atoms of about 1E21 cm⁻³ and extends from said first surface into said silicon carbide wafer to a depth of about 500 Angstroms.
 78. An LED according to claim 60 wherein the peak concentration of implanted atoms in said implanted region occurs at or near the first surface of said silicon carbide substrate.
 79. A light emitting diode (“LED”) comprising: a silicon carbide wafer having a first and second surface and having a predetermined conductivity type and an initial carrier concentration; a conductive buffer region on the first surface of said silicon carbide substrate; a region of implanted dopant atoms having the same conductivity as said wafer and extending from said first surface into said silicon carbide wafer for a predetermined distance causing a reduction of the overall forward voltage drop observable at the interface between said wafer and said conductive buffer region; an active region on said conductive buffer region; an ohmic contact to said active region; and an ohmic contact on said second surface of said silicon carbide substrate.
 80. An LED according to claim 79 wherein said implanted region has a peak concentration of implanted dopant atoms of between about 1E19 and 5E21 cm⁻³.
 81. An LED according to claim 79 wherein said implanted region has a thickness of between about 10 and 5000 Angstroms.
 82. An LED according to claim 79 wherein said implanted region has a peak concentration of implanted dopant atoms of about 1E21 cm⁻³ and is about 500 Angstroms thick.
 83. An LED according to claim 79 wherein said implanted region is doped with atoms selected from the group consisting of nitrogen and phosphorus.
 84. An LED according to claim 79 wherein said implanted region comprises phosphorus donor atoms implanted with first dose at a net dopant concentration of 2E15 cm⁻² at an energy of 25 keV and a second dose at a net dopant concentration of 3.6E15−2 at an energy of 50 keV.
 85. An LED according to claim 79 wherein said region of implanted dopant atoms extends into said substrate to a depth of between about 800 and 1000 Angstroms.
 86. An LED according to claim 79 wherein said active region is a single heterostructure. 87 An LED according to claim 79 wherein said active region is a double heterostructure.
 88. An LED according to claim 79 wherein said active region is a single quantum well.
 89. An LED according to claim 79 wherein said active region is a multiple quantum well.
 90. An LED according to claim 79 wherein said silicon carbide wafer comprises n-type 6H-silicon carbide having an initial ion concentration of nitrogen donor atoms of between about 5E17 and 3E18 cm⁻³ and wherein said region of implanted dopant atoms comprises phosphorus dopant atoms with an implant concentration of between about 1E19 and 5E21 cm⁻³ and is about 500 Angstroms thick.
 91. An LED according to claim 79 wherein said silicon carbide wafer comprises n-type 6H-silicon carbide having an initial ion concentration of nitrogen donor atoms of between about 5E17 and 3E18 cm⁻³ and wherein said region of implanted dopant atoms comprises nitrogen dopant atoms with an implant concentration of between about 1E19 and 5E21 cm⁻³ and is about 500 Angstroms thick.
 92. An LED according to claim 79 wherein said silicon carbide wafer comprises n-type 4H-silicon carbide having an initial ion concentration of nitrogen donor atoms of between about 5E17 and 3E18 cm⁻³ and wherein said region of implanted dopant atoms comprises phosphorus dopant atoms with an implant concentration of between about 1E19 and 5E21 cm⁻³ and is about 500 Angstroms thick.
 93. An LED according to claim 79 wherein said silicon carbide wafer comprises n-type 4H-silicon carbide having an initial ion concentration of nitrogen donor atoms of between about 5E17 and 3E18 cm⁻³ and wherein said region of implanted dopant atoms comprises nitrogen dopant atoms with an implant concentration of between about 1E19 and 5E21 cm⁻³ and is about 500 Angstroms thick.
 94. A method of treating a silicon carbide substrate for improved epitaxial deposition suitable for use as a precursor in the manufacture of devices such as light emitting diodes, the method comprising: forming a capping layer on the first surface of a conductive silicon carbide wafer from a material that may be controllably deposited in thin layers, can be implanted with ions having the same conductivity as the silicon carbide wafer, and can be removed without substantially damaging the underlying surface of the wafer; implanting dopant atoms of a first conductivity type into and through the capping layer and into the silicon carbide wafer at one or more predetermined dopant concentrations and implant energies to form a dopant profile; annealing the implanted wafer; removing the capping layer; and growing an epitaxial layer on the implanted first surface of the substrate wafer.
 95. The method according to claim 94 comprising growing the capping layer to a thickness such that the maximum implant concentration of dopant atoms within the silicon carbide wafer resulting from the implantation step is at or near the interface between the capping layer and the wafer.
 96. The method according to claim 94 comprising implanting at doses and energies such that the resulting implant profile at the surface of the silicon carbide wafer is about 1E21 cm⁻³ and remains relatively flat for a depth into the wafer of about 500 Angstroms.
 97. The method according to claim 94 comprising implanting the doses at less than about 5E21 cm⁻³ to prevent undesirable damage to the crystal lattice of the silicon carbide wafer. 